1. Related Technical Fields
Related technical fields include guidance apparatuses, route guidance methods, and computer programs for guiding movable bodies along navigation routes.
2. Related Art
Recently, navigation systems that provide driving guidance for vehicles have been installed in many vehicles so that the drivers can easily reach desired destinations. The navigation systems herein refer to devices capable of detecting the current positions of the vehicles in which the navigation systems are installed using, for example, GPS receivers, capable of acquiring map data corresponding to the current positions via recording media such as DVD-ROMs and HDDs or via networks, and capable of displaying the map data on liquid crystal monitors. Such a navigation system has a route search function of searching for an optimum route from a place of departure to a destination on the basis of a desired destination input by a user. The navigation system displays a navigation route set on the basis of the search results on a display screen, and provides the user with guidance using voice and the display screen when the vehicle approaches an intersection at which the user is to be instructed to, for example, turn right or left (hereinafter referred to as “guidance intersection”) so as to guide the user to the desired destination without fail. Recently, some devices such as cellular phones, personal digital assistants (PDAs), and personal computers have also been provided with functions similar to those of the navigation system, and are capable of providing guidance described as above for pedestrians and two-wheeled vehicles in addition to the vehicles.
When the user is instructed to turn right or left at the guidance intersection, it is important for the user to correctly determine a road for which the vehicle leaves the guidance intersection (that is, a road from which the user enters the guidance intersection) among a plurality of roads connected to the guidance intersection. However, when the guidance intersection has a complicated shape such as that of a junction of five roads, it is difficult for the user to determine the road for which the vehicle leaves the guidance intersection on the basis of the guidance. To solve this, Japanese Patent Application Publication No. JP-A-2005-147697 (in pages 7 and 8 and FIGS. 5 and 6), for example, describes a technology of guiding a user using voice guidance messages selected by the user. In this technology, when the vehicle approaches a guidance intersection having a complicated shape, the user is required to select a voice guidance message from a list of voice guidance messages to be provided at the guidance intersection displayed on a display screen. After this, the user is guided using the voice guidance message selected by the user each time the vehicle approaches the same guidance intersection.
The technology described in JP-A-2005-147697 allows the user to determine the road for which the vehicle leaves the guidance intersection that the vehicle has passed before on the basis of the guidance. However, the technology cannot be applied if the vehicle has never passed the guidance intersection. In addition, selection of a voice guidance message required each time the vehicle passes a guidance intersection having a complicated shape is burdensome on the user during driving.